Abrasive medium comprising short fibers in the synthetic resin binder

ABSTRACT

An abrasive medium including a layer of abrasive particles attached to a synthetic resin-impregnated fiberglass mat backing by a synthetic resin binder wherein either or both of said resins contain short fibers of about 0.003-0.012 mm. diam. and 0.1 to approx. 3 mm. length, the fibers being of glass, asbestos, ceramic material or graphite in an amount of between about 2-20 percent by weight based on the solid resin material.

United States Patent 1191 Holzhauer 1 1 Oct. 2, 1973 1 1 ABRASIVE MEDIUM COMPRISING SHORT 3.529.945 9/1970 Charvat 51/295 FIBERS [N THE SYNTHETIC RESIN BINDER 2,880,080 3/1959 Rankin C1211 51/298 2362.806 12/1958 Nestor v. 51/295 [75] Inventor: Ru lf fl lzh 2,284,716 6/1942 Benner (31111- 51/2981 Marienheide/Rh1d'., Germany [731 Assignee: Firm? August Ruggeberg Primary Examiner-D0na1d J. Arnold Manenhelde/Rhld" Germany Att0rney-Br0wdy & Neimark {22] Filed: Feb. 16,1971

211 App1.Nn.: 115,164

1 [57] ABSTRACT 130] Foreign Application Priority Dam An abrasive medium including a layer ofubrusive parti y Gcrmany P 29 25 294-4 cles attached to :1 synthetic resin-impregnated fiberglass mat backing by a synthetic resin binder wherein [52] [1.5. CI. 51/298, 51/295 either or both of Said resins Contain Short ib f [51] Int. Cl C08g 51/12, C08h 17/12 about 0 003 2 diam and 0 to approx 3 [58] Field of Search 51/293, 295, 296, mm, length, the fibers being 6f glass, asbestos Ceramic 51/298 297 material or graphite in an amount of between about 1 2-20 percent by weight based on the solid resin mate- [56] References Cited rial.

UNITED STATES PATENTS 10/1956 11 Claims, 2 Drawing Figures Hurst- 51/293 ABRASIIVE MEDIUM COMPRISING SHORT FIBERS IN THE SYNTHETIC RESIN BINDER The invention concerns an abrasive medium made up of abrasive particles attached to a base, such as abrasive paper, abrasive cloth, endless abrasive belts, socallcd fiber abrasives and the like. It is advantageous that these abrasives be as flexible as possible. At the same time, it is necessary for the abrasive grain layer on the backing to be attached so firmly to the latter that even when the flexibility of the backing is exhausted, premature detachment of thebarasive grains can be avoided as much as possible.

In the past, the backing for such abrasive media has consisted of paper, cotton, synthetic silk or nylon cloth, or vulcanized fiber. A disadvantage of previous abrasive media is that the backing materials known heretofore have only a limited temperature resistance. Hence, the selection of resins with which the abrasive grains are attached to the base, with consideration of the backing, is limited to those types which can be set satisfactorily at maximum temperatures of approximately 120 130 C. However, since much higher temperatures are developed in the grinding process when working at a high rate of metal removal, it is advantageous to use bases which can themselves withstand higher temperatures and permit the use of those adhesive resins that set at temperatures of l80 and thereabouts, with an eye toward their strength.

Another shortcoming of the heretofore conventional bases is to be seen in the fact that these heretofore employed backings are largely sensitive to climatic conditions.

An object of the present invention is to overcome th hereinbefore mentioned shortcomings of previously used base materials. Thus, abrasive particles are to be affixed to a base which possesses an especially high degree of flexibility and yet, despite this high flexibility, ensures a firm anchoring of the abrasive particles in the base. The backing materials to be used should be indifferent to climatic conditions and withstand high temperatures even at high operating speeds. In this connection, the synthetic resins used to bind the abrasive grains should set at temperatures of about 180 C. and above. In this regard, synthetic resins may be selected which ensure an improved flexibility even after setting.

Accordingly, the present invention first consists in the fact that a fiberglass mat serves as the fibrous backing material, and that the impregnating synthetic resin for the fiberglass mat may contain short fibers of glass, other, ceramic material, asbestos, graphite or similar materials.

The synthetic resin acting as the binder for the abrasive grains may also contain these short fibers. Thus the short fibers may be included in either the synthetic resin impregnating the fiberglass mat or in the synthetic resin binding the abrasive grains to the mat or in both resins.

Preferably these short fibers are short fibers of fiberglass, with a length of several tenths of a millimeter to severalmillimeters. In using these short glass fibers, it is advantageous for the latter to have a length of a few tenths of a millimeter and a diameter of 0.003-0.012 mm. The short glass fibers can preferably be added in amounts between 2 and 20 percent by weight, basedon the solid resin material. I

When suitable elastic resin impregnations are chosen, the fiberglassmat-resin base is very flexible.

This fiberglass-resin combination is also insensitive to climatic conditions, since the glass fibers do not change their mechanical characteristics under the influence of moisture, as is the case with the vegetable fibers used in conventional bases such as paper, cotton cloth and vulcanized fiber. This fact also results in the abrasive medium according to the present invention being also especially well suited for wet grinding.

If short fibers of the above mentioned type are enclosed according to the invention in the binder for the abrasive grains and/or in the impregnating resin for the fiberglass mat, the adhesive strength of the abrasive grain binder layer will be increased to an unexpectedly high degree.

The short fibers, preferably the short glass fibers, in the present case have the effect of micro-reinforcement or bridge formation, which has the effect that the ad hesion of the abrasive grains to the fiberglass mat base is significantly improved. In view of the especialy high flexibility of the abrasive medium, the adhesion of the synthetic resin binding the abrasive grains to the backing is subjected to especially high stress. This, in connection with the fact that the bond of the synthetic resin to the non-absorbent fiberglass surface is also difficult, shows the significance of optimum adhesion of the abrasive grains to the fiberglass mat base, obtainable according to the invention even under very severe thermal and flexion stress of the abrasive medium.

It has been shown that the abrasive medium prepared according to the present invention has not only an extraordinary abrasive resistance, abrasive quality, blast resistance and thermal capacity, but also an extremely high durability and resistance to alternating flexion, even with the most severe deformation. Thus, it was shown that prolonged stress on a conventional abrasive backing using vulcanized fiber with a diameter of 178 mm. and corundum grain size 24, with a lateral deflection of about l0 mm. developed a crack due to fatigue of the backing after l50,000 load cycles. When the fiberglass mat according to the invention, including the short fiber reinforcement in the binder, was used under the same conditions, the abrasive on the base was still intact after 1.5 million load cycles.

The effect of the high prolonged alternate flexion stress resistance was also aided by the fact that the short glass fibers, like the fiberglass elementary fibers of the fiber sections in the mat base, as well as the abrasive grains, were treated with adhesive agents which consist mainly of monomer silicon compounds generally known in the trade as Silanis. This Silan treatment also increases considerably the resistance of the abrasive medium according to the present invention to the effect of moisture, which is especially important in wet grinding.

This surprisingly good result, however, is also influenced by the fact that in accordance with this invention the fiberglass mat that is used consists of fiber elements that are stretched out straight as fiber sections and ori ented in all directions. This gives the fiberglass mat, despite its high flexibility, the same strength in all stress directions.

The drawing shows a form of construction of the abrasive medium according to the invention, and is arranged as follows:

FIG. 1 is a top view of an abrasive medium whose base is punched out in disk form from a fiberglass mat,

the structure of the individual fiber elements in the base is indicated schematically in one section; and

FIG. 2 is a cross sectional view of a transverse cut through a portion of an abrasive medium as in FIG. 1, considerably magnified.

The base 3 of the abrasive medium consists of a disk of fiberglass material with a glass fiber weight of approximately 200 to 1,000 grams/m The individual fiber elements consist of fiber segments 50 to 100 mm. long. These fiber segments can be in the-form of clustered fiber segments 1 or individual fiber segments 2. These fiber segments, about 50 100 mm. long, are stretched out straight and are oriented in all directions. The fibers are not bent and not snaked around each other, as is the case in fiberglass cloth. A fiberglass mat disk of this kind is extremely porous and flexible.

The disk base is impregnated thoroughly with a synthetic impregnating resin. In this state, the porous texture of this base is dense enough to prevent the abrasive grains 4 placed on the surface from falling through.

These abrasive grains 4, which are preferably treated beforehand with an adhesion agent as discussed earlier, are soaked with a resin coating before being placed on the base; this is intended to ensure a positive anchoring on the base and an inner bond with the impregnating resin in the fiberglass mat.

Short glass fibers are incorporated in the impregnating resin layer 7 for the fiberglass mat base, and/or in the synthetic resin with which the abrasive grains 4 are surrounded. The diameter of these short glass fibers, which are already known for their use in strengthening fiberglass plastics, is about 0.003-0.0l2 mm. The individual fiber elements have a length of 0.1 to approx. 3 mm. The amount of short glass fibers added may be 2 to percent by wt., based on the solid resin content. The short glass fibers are labelled 6 in FIG. 2. The binders used may be based on epoxy, polyester, melamine or preferably on phenol resin, and specially elasticized.

These abrasive media can be used on an unlimited basis in wet grinding processes, which are known to give an especially good finish.

The addition of short glass fibers may also be combined with powdered fillers such as marble dust (CaCO cryolite Na (AlF pyrite (FeS iron oxide (FeO, Fe O and the like. The mechanical and thermal properties of the abrasive medium can be influenced within broad limits by these fillers. It is to be understood that the term ceramic material as used in the present specification and claims is intended to be generic to glass.

It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification.

What is claimed is:

1. In an abrasive medium comprising a layer of abrasive particles bonded by means of a thermosetting synthetic resin binder to a backing comprising a mat of glass fibers impregnated with a thermosetting synthetic resin, the improvement comprising uniformly incorportating into said synthetic resin binder extremely short fibers having a length of from about 0.1 to about 3mms. and a diameter of from about 0.003 to 0.012 mm., and being of a material selected from the group consisting of asbestos, ceramic material and graphite.

2. An abrasive medium according to claim 1, wherein said short fibers are present in an amount of between about 2 and about 20 percent by weight on the solid synthetic resin material.

3. An abrasive medium according to claim 1, wherein said improvement further comprises uniformly incorporating said short fibers in the synthetic resin used for impregnating the glass fiber mat.

4. An abrasive medium according to claim 3, wherein the short fibers are present in the said synthetic resin used for impregnating the glass fiber mat in an amount of between about 2 and about 20 percent by weight based upon the solid synthetic resin material.

5. An abrasive medium according to claim 1, wherein the glass fibers forming the said backing mat have a length of between about 50 and about l00mms.

6. An abrasive medium according to claim 1, wherein said synthetic resin binder contains a finely powdered inert filler.

7. An abrasive medium according to claim 3, wherein said synthetic resin impregnating said glass fibers contains a finely powdered inert filler. v

8. An abrasive medium according to claim 1, wherein said glass fibers are randomly oriented.

9. An abrasive medium according to claim 1, wherein said synthetic resin binder comprises a synthetic resin which sets at a temperature of at least C.

10. An abrasive medium according to claim 2, wherein said short fibers are ceramic and said ceramic short fibers are made of glass.

11. An abrasive medium according to claim 4, wherein said short fibers in both the synthetic resin binder and the synthetic resin used for impregnating the glass fiber mat are ceramic and said ceramic short fibers are made of glass. 

2. An abrasive medium according to claim 1, wherein said short fibers are present in an amount of between about 2 and about 20 percent by weight on the solid synthetic resin material.
 3. An abrasive medium according to claim 1, wherein said improvement further comprises uniformly incorporating said short fibers in the synthetic resin used for impregnating the glass fiber mat.
 4. An abrasive meDium according to claim 3, wherein the short fibers are present in the said synthetic resin used for impregnating the glass fiber mat in an amount of between about 2 and about 20 percent by weight based upon the solid synthetic resin material.
 5. An abrasive medium according to claim 1, wherein the glass fibers forming the said backing mat have a length of between about 50 and about 100mms.
 6. An abrasive medium according to claim 1, wherein said synthetic resin binder contains a finely powdered inert filler.
 7. An abrasive medium according to claim 3, wherein said synthetic resin impregnating said glass fibers contains a finely powdered inert filler.
 8. An abrasive medium according to claim 1, wherein said glass fibers are randomly oriented.
 9. An abrasive medium according to claim 1, wherein said synthetic resin binder comprises a synthetic resin which sets at a temperature of at least 180* C.
 10. An abrasive medium according to claim 2, wherein said short fibers are ceramic and said ceramic short fibers are made of glass.
 11. An abrasive medium according to claim 4, wherein said short fibers in both the synthetic resin binder and the synthetic resin used for impregnating the glass fiber mat are ceramic and said ceramic short fibers are made of glass. 